Related Rule
Canada
Practice Relating to Rule 137. Participation of Child Soldiers in Hostilities
Canada’s LOAC Manual (1999) provides, with respect to non-international armed conflicts in particular: “Children are to receive such aid and protection as required including: … a ban on their … participation in the hostilities while under the age of fifteen”. 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, p. 17-3, § 22.
The manual adds: “Children under fifteen who do take part in hostilities remain protected.” 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, p. 17-3, § 23.
Canada’s LOAC Manual (2001) states in its chapter on non-international armed conflicts:
1. [The 1977 Additional Protocol II] provides that children are to receive such aid and protection as required including:
c. a ban on their enlistment or participation in the hostilities while under the age of fifteen.
2. Children under fifteen who do take part in hostilities remain protected. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 1714.1.c and 2.
Canada’s National Defence Act (1985) states: “A person who is under the age of eighteen years may not be deployed by the Canadian Forces to a theatre of hostilities.” 
Canada, National Defence Act, 1985, Section 34.
Canada’s Crimes against Humanity and War Crimes Act (2000) provides that the war crimes defined in Article 8(2) of the 1998 ICC Statute are “crimes according to customary international law” and, as such, indictable offences under the Act. 
Canada, Crimes against Humanity and War Crimes Act, 2000, Section 4(1) and (4).
In 2013, in the MJS case, Canada’s Federal Court dismissed an appeal against the applicant’s exclusion from refugee protection on grounds of complicity in war crimes and crimes against humanity. The Court stated:
[T]he Panel found that “the documentary evidence clearly demonstrates that [the Group] committed crimes against humanity as well as war crimes in the period 1998 to 2005”, by, for example, using child soldiers. 
Canada, Federal Court, MJS case, Reasons for Judgment and Judgment, 20 March 2013, § 22.
In 2013, in the Sapkota case, Canada’s Federal Court dismissed a request for review of a decision denying refugee protection to the applicant on grounds of complicity in crimes against humanity in Nepal between 1991 and 2009. While reviewing the submissions of the respondent, Canada’s Minister of Citizenship and Immigration, the Court stated: “The Respondent notes that the Rome Statute of the International Criminal Court … is endorsed in Canada as a source of customary law.” 
Canada, Federal Court, Sapkota case, Reasons for Judgment and Judgment, 15 July 2013, § 28.
At the 27th International Conference of the Red Cross and Red Crescent in 1999, Canada pledged “to promote the adoption of national and international standards prohibiting the military … participation in armed conflicts of persons under 18 years of age”. 
Canada, Pledge made at the 27th International Conference of the Red Cross and Red Crescent, Geneva, 31 October–6 November 1999.
In 2012, in its written replies to the issues raised by the Committee on the Rights of the Child with regard to Canada’s combined third and fourth periodic reports, Canada stated:
Extraterritorial jurisdiction for violations of the provisions of the [2000] OPAC [Optional Protocol on the Involvement of Children in Armed Conflict]
186. Canada generally does not extend its jurisdiction to prosecute offences committed by Canadians or permanent residents abroad unless required to do so by treaty obligations. No such justification exists in the case of violations of the provisions of the OPAC.
187. Nevertheless, Canada adopted the Crimes Against Humanity and War Crimes Act in 2000 implementing the Rome Statute, by which authors of genocide, crimes against humanity and war crimes, including that of “conscripting or enlisting children under the age of 15 years or using them to participate actively in hostilities,” may be prosecuted for that offence if present in Canada after the time the offence is alleged to have been committed.
Age of voluntary recruitment
190. … As provided by section 34 of the National Defence Act, the Canadian Forces do not under any circumstances deploy persons under the age of 18 into areas where hostilities are taking place. 
Canada, Written replies by the Government of Canada to the Committee on the Rights of the Child concerning the list of issues to be taken up in connection with the combined third and fourth periodic reports of Canada, 21 January 2013, UN Doc. CRC/C/CAN/Q/3-4/Add.1, submitted September 2012, §§ 186–187 and 190.